Detecting Keypoint of 3D model, and distance between them
It depends on the format of your 3D model dataset , if your dataset is made of cad models you could voxelize your dataset and train a convolutional neural network on it , but it could be very time consuming to train 3D convnets . instead you could use a multi view 2D CNN https://arxiv.org/abs/1505.00880?context=cs